Frequency stabilizing system



Nov. 29, 1932. w. T. WINTRINGHAM FREQUENCY STABILIZING SYSTEM Filed Feb. 17,

` Mtl/Joris Patented Nov. 29, 1932 UNITED STATES'.v

PATENT OFFICE y WILLIAM T. WINTRINGHAM, OIF BROOKLYN, NEW. YORK, ASSIGNOR TO AMERICAN .TELE- PHONE .AND TELEGR-APH COMPANY, A CORPORATION OF NEW YORK FREQUENCY s'rABIL-IZING SYSTEM Application filed February 17, 1930. Serial No. 429,153.

This invention relates generally to alternating' current generators. More particularly, this invention vrelates to arrangements for producing alternating current of highly lconstant frequency.

be substantially `affected by heat or thermal edects. However, with `all the refinement of oscillator technique, there still remain small variations in frequency caused by slight variations in temperature andl battery variations, as well as other uncontrollable.factors. It is the object of this invention to provide arrangements whereby variations in the frequency of an oscillator, resulting yfrom the factors above mentioned, may be substantially reduced.

This invention will be better understood from the detailed description hereinafter following when read in connection with the accompanying drawing, in which Figure l shows an arrangement for controlling the frequency of an oscillator, and Fig. 2 shows apparatus for producing the rotation of a mo-l torin one direction or the other in order to increase or decrease the frequency of the current which may be derived from'an asso-7 ciated oscillator.

Referring to Fig. l of the drawing, there are shown two standard oscillators designated O1 and O2 which are designed to maintain as high stability in their frequency characteristics as is possible. These oscillators may, of course, be of any vwell known type, preferably of some vacuum tube type, to each of which a piezo-electric device may be connected in order that the frequencies of the currents produced thereby may be maintained constant within very narrow limits.

The reference character O3 designates an oscillator of nominal frequency stability the frequency of which maybe varied in eitherv direction by a change in one or more of the' elements of its structure. For the purpose of illustration the oscillator O3 may be of a resistance feed-back type, the frequency of which may be changed over a substantial, though limited range by varying one of its capazitative elements, for example, condenser 1.

- The oscillator O3 includes a three-element vacuum tube V1 ofk any well known type.v The grid electrode of this vacuum tube is connected toits filament electrode through a winding Ll and a battery B1. The plate electrode of vacuum tube V1 is connected to the filament electrode through a battery B2 anda choke coil L2, the battery B2 providing the proper operating potential for the pla-te electrode of thevacuum tube system. All of the resistance of a potentiometer P is interposed' between the plate and filament electrodes of the vacuum'tube V1. All of the current de-V rived from the oscillator is impressed across the entireresistance of potentiometer P, and the voltage of this current may be controlledv by the adjustment of the associated variable element of the potentiometer.

The oscillator O3 also includ-es a parallel tuned circuit consisting of two condensers C1 and C2 and the winding L3, which is inductively coupled to the winding Ll. lThe lower terminals of both windings L1 and L3 a-reconnected to each other. Condenser C2 may be invariable in its capacitative value, while condenser C1 may be varied in its capacitative value to any desired extent within reasonable limits by changing the spacing between its component elements. Current isV fed from the plate circuit of the vacuum tube Vl'to the parallel tuned circuit through a resistance R1 and acondenser C3.,

The oscillator O3 may be one which ordi narily produces current of some definite frerated from those of the rotor by a dielectric such, for example, as air. It is the rotor which may be adjusted in its position with respect to the stator to effect any desired change in the frequency of the current produced by the oscillator when that frequency departs from the assigned value. It will be understood that the oscillator O3 may be of any well known type to which a piezo-electric structure may be connected, the vibratory period of the piezo-electric element of which may be changed by a corresponding change in the surrounding temperature, so that the frequency of the generated current may be controlled merely by an adjustment in the temperature of the surrounding medium.

A vacuum tube of the three-electrode typ-e, designated V2, is employed to amplify the current derived from oscillator O3. The grid electrode of tube V2 is connected to the filament electrode through a battery B2 and a portion of the resistance of potentiometer l). The plate electrode of the latter tube is connected to the filament electrode through a battery B4 and an element of inductance to be subsequently described. Vacuum tube V2 amplifies the current derived from oscillator O3 in a well known manner.

The current generated by the oscillator O3 and amplified by the vacuum tube V2 is transmitted to demodulators D1 and D2 through a hybrid coil arrangement H. The hybrid coil arrangement may consist of a plurality of windings inductively related to each other, as shown. The winding L4 may be connected between the plate electrode of vacuum tube V2 and the positive terminal of battery B1. rlhe windings L5 and L1s may be connected to demodulator D1 and in series with each other. The windings L7 and L8 may be connected to demodulator D2 and in series with each other. The winding L1, may be connected to a balancing network N which may be of any type well known in the art.

urrent derived from oscillator O1 is transmitted directly to demodulator D1, and this current may have a frequency f1. Current derived from oscillator O2 is directly transmitted to demodulator D2, and this current may have a frequency f2. rlhe balancing network N connected to the hybrid coil arrangement H is so adjusted that the current supplied by oscillator O1 to the demodulator D1 cannot reach demodulator D2, and conversely, the current supplied to demodulator D2 by oscillator O2 cannot reach demodulator D1.

In accordance with the accepted theory of demodulation, the output of demodulator D1 will contain, among other components, current of the frequency ,f1-f2. Similarly, there will be found in the output of demodulator 4D2 current of the frequency )f2-#3', among Y other components. VCurrents having frequencies different from the values )e1-f3 and )f2-f3 may, if desired, be suppressed in any well known manner.

A selective network designated T1 interconnects the demodulator D1 with the grid circuit of a vacuum tube V3 which is employed for the purpose of current rectification. A similar selective network designated T2 is connected between demodulator D2 and the grid circuit of a vacuum tube V4 which is also employed for rectifying impressed current. The selective network T1 may be one of those'shown in an article authorized by Otto J. Zobel in the Bell System Technical Journal for July, 1928, entitled Distortion correction, for example, the one shown at page 515 of the article. The selective network T2 may assume the character of another of those shown in the article ust mentioned, the one shown at page 525 being suitable for this purpose. lf the networks shown in the article just mentioned are used, it will be necessary to interconnect the networks` T1 and T2 with the grid circuits of the vacuum tubes V3 and V1 bymeans of transformers, in a well known manner.

t is a property of the selective network T1 i that the voltage impressed upon the grid electrode of the vacuum tube V3 will increase almost lineally asthe frequency in-l creases. Similarly, the property of the selective network T2 is such that the voltage impressed upon the grid electrode of the vacuum tube V4 will decrease almost lineally as the frequency )c2-f3 increases. By employing batteries B5 and B6 of the proper voltages, it will be possible to operate the vacuum tubes V3 and V4, respectively, as rectiiers, so that any increase in the effective potentials of the grid electrodes of vacuum tubes V3 and V4 will cause corresponding increases in the effective thermionic emissions between the filament and plate electrodes of these tubes. Of course, a decrease in the effective potentials of the grid electrodes of the vacuum tubes V8 andVA1 will cause corresponding decreases in the currents flowing in their respec tive plate circuits. v

A differential polar relay A0 includes two widings L11 vand L12 which are directly connected in the plate circuits of the vacuum tubes V3 and V1, respectively. rlhe battery B7 is connected to the plate electrodes of the tubes V3 and V.1 through the windings L11 and L12. Under normal conditicns'the current derived from battery B7 divides equally between windings L11 and L12, and since these windings produce mutually opposite magnetic fields, the armature M of relay A0 will be normally unaffected by the Huxes produced by these currents. The armature M is preferably one which is permanently magnetized, and moreover, it normally remains midway between contacts'd1 and cl2. When the current of the frequency f1-f3 impressed upon lijf).

les

the selective network T1 becomes greater than the current of the frequency )f2-f3 impressed upon the selective network T2, then the plate current of the vacuum tube V3 will be greater than the plate current of the vacuum tube V1, and the flur` produced by winding L11 will be greater than that produced by winding L12. In that event the armature M will become attracted so as to close contact (Z1. If, on the other hand, the plate current of the vacuum tube V4 becomes greaterl than the plate current of the vacuum tube V3, then the flux produced by the winding L12 will be greater than that produced by the winding L11 and the armature M will be repelled and it will close contact (Z2. l

When armature M closes contact (Z1, apparatus designated G1 will be operated in order to increase the frequency of the current produced by oscillator O3. When armature M closes contact (Z2, apparatus designated G2 will be operated to decrease the frequency of the current produced by oscillator O1. rl`he battery BS may be employed for supplying the current required to energize either of the arrangements G1 or G2.

If the frequency of the oscillator 03 increases by a small amount, then the frequency )e1-f3 of the current derived from the demodulator D1 will decrease, decreasing the effective po-tential of the grid electrode of the vacuum tube V3 and correspondingly decreasing the flow of current from battery B7 through the winding L11 of the plate circuit of vacuum tube V3. Similarly, the frequency f2 f3 of the current derived from the demodulator D2 will decrease, increase ing the effective potential on the grid elec-v trode of the vacuum tube V1 and correspondingly increasing the flow of current through the winding L12 in the plate circuit of the vacuum tube V1. Then the armature M will close contact (Z2, operating the apparatus G2 in order to decrease the frequency of the oscillator O3.

If the frequency of the oscillator O1 increases by a small amount, then the frequency of the current transmitted by demodulator D1 of frequency )f1-f3 increases, correspondingly increasing the effective potential impressed upon the grid electrode of the vacuum tube V3 and correspondingly increasing the current flowing in the plate circuit of vacuum tube V3 through the winding L11 of the differential polar relay. The armature M will then close contact (Z1, setting into operation the apparatus G1 in order to increase the frequency of the oscillator O3. However, as the frequency of oscillator O3 increases, then the currents of the frequencies f1-f3 and )f2-f3 transmitted by demodulators D1 and D2, respectively, both change, and the system will reach stability when the 'v frequency of oscillator O3 has increased by an amount slightly less than one-half of the increase in the frequency of oscillator O1.

If the frequencies of oscillators O1 and O2 both increase by the same amount, then the currents of frequencies )c1-f3 and f2--f3 will both increase equally. However, the current flowing through the winding L11 will be greater than that flowing through winding L12, and therefore the armature M of the differential polar relay will close contact (Z1. The apparatus G1 will then be set into operation to increase the frequency of the oscillator O3 to the same extent that the frequencies of oscillators O1 and O2 have changed.

When the frequency of oscillator O1 increases by a certain amount andthe frequency of oscillator O2 decreases by the same amount, then the values f1-f3 and 7a2-f1 will respectively increase and decrease by equal amounts. In that event the flow of current through the Winding L11 will be increased by a certain amount and the flow of current through winding L12 will be increased by the same amount. The armature M of the differential polar relay will then remain in its mid-position, and there will be no change in the frequency of the oscillator O2.

It will be apparent that the principles of this invention relate to arrangements whereby the current of a given oscillator will change in frequency by an amount which is the mean between the changes of the frequencies of two independent stand ard oscillators. Clearly, the constancy of the frequency of the given oscillator will be greatly superior to that constancy which may be derived from a single oscillator to the extent that the mean of two standard oscillators may be more nearly correct than either one individually. If the'two standard oscillators are designed to have equal and opposite changes in frequency for equal changes in temperature and battery potentials, then the frequency of the controlled oscillator will be practically invariable with these changes, and onlv the random frequency variationsof the standard oscillators will tend to change the frequency of the controlled oscillator.

Fig. 2 shows apparatus driven by a motor which may, for example, be used to change the capacity of the condenser designated C1 of the oscillator O3. The motor of this arrangement is of the direct current type including a field winding designated L20 and an armature S, with which brushes c1 and e2 are associated. The armature of the motor may be on the same shaft or be otherwise coupled to a worm W which controls the rotation of a gear pinion U. When the armature S of this motor rotates in a -clockwise direction, the pinion U will be rotated in one direction, and when the armature is rotated in a counter-clockwise direction, the pinion Will be moved in the opposite direction. Each revolution of the Worm W Will advance the pinion U by one tooth.

lVhen the armature M is in its mid-position, neither of tvvo relays designated A1 and A2 will be operated. llhen armature M closes contact d1, relay A1 will be operated by current flowing from a battery B through the Winding of relay A1, Contact D2,

armature M and ground. lhen contact Z2 is closed by armature M, relay A2 Will become operated, current then flowing from battery B20 through the Winding of relay iA2, contact d2, armature M and ground.

W hen the relay A1 is operated, the armature S of the motor Will be rotated in one direction, and when the relay A2 is operated, armature S will be rotated in the opposite direction, because of the fact that the polarity of the potential of source X applied to the field Winding L20 of the motor will then be reversed.

When relay A1 is operated., the brush el I Will be connected to the negative side of the source X through a circuit Which includes conductor 2l, armature cl, conductor 22 and conductor 23. rlhe upper terminal of the field coil L20 will be connected to the positive side of source X through a circuit Which includes conductor 2A, armature Z1 and conductor 25. rlhe lower terminal of field coil L20 Will be connected to the negative side of A source X through a circuit which includes 0 conductor 28.

j of the field coil L20 Will be connected to the positive side of source X through a circuit Which includes conductor 30, armature Z2 and conductor 25. lt Will then be seen that the operation of relay A2 Will reverse the polarity impressed upon the field coil L20. ln

that event the armature S Will be rotated in a counter-clockwise direction.

lt Will be noted that the relays A1 and A2 are employed for the purpose of reversing the polarity of the source X impressed upon the i eld coil L20 of the motor. It Will be further noted that the negative terminal of the source X is connected to the brush el through either armature ,zal or armature k2, depending upon Whether relay A1 or relay A2 has operated.

The brush E2 is always connected to the positive side of the source X.

Vilhile this invention has been shovvn and described in a certain particular arrangement merely for the purpose of illustration, it Will be understood that the general principles of this invention may be applied to other and Widely varied organizations Without departing from the spirit of the invention and the scope of the appended claims.

l/V hat is claimed is:

l. rlhe method of controlling the frequency of a current of variable frequency Which consists in generating tvvo currents of the same frequencies and Which are highly constant in their frequencies, producing a first direct current which varies in amplitude in accordance with the difference between the frequencies of one of the generated currents and the current to be controlled, producing a second direct current which varies in amplitude in accordance With the difference in the frequencies between the other of the generated currents and the current to be controlled, increasing` the frequency of the current to be controlled when the first direct current is greater in amplitude than the second direct current, and decreasing the frequency of the current to be controlled when the amplitude ofthe g second direct current is greater than the first direct current.

2. A frequency control system for a gencrater which is variable in frequency and which. is to be controlled as te its frequency, comprising means fer independently generating currents of the same frequencies and which are highly censtant in their frequencies, means coupled to the generator of variable frequency said generating means for producing` a first direct current Which varies in accordance With the difference in the frequencies between the current of the generator to be controlled and one of the currents of said generating means, means coupled to the generator of variable frequency and said generating means for producing a secend direct current which varies in accordance with the difference in the frequencies between the current of the generator to be controlled and the other current of said generating means, means including a differential polar relay for increasing the frequency of the current of the generator to be controlled when the amplitude of the first direct current exceeds the amplitude of the second direct current, and means including said differential polar relay for decreasing the frequency of the current of the generator to be controlled when the amplitude of the second direct current exceeds the amplitude of the first direct current.

3. A frequency control system comprisingl tvvo standard oscillators producing currents of the same frequencies, a third oscillator including a reactive element of adjustable magnitude which is variable so as to control the frequency of its sustained oscillations, means to independently beat the current of each of the standard oscillators with the current of the third oscillator in order to produce two currents having frequencies equal to the differences between the frequencies of the pairs of currents independently beaten, means to convert each of the currents resulting from the beating process into a direct current of an amplitude depending upon the frequency of the current resulting from the beating process, and means including a differential polar relay responsive to the greater of the direct currents to control the frequency of said third oscillator.

4. A frequency control system comprising two standard oscillators producing currents of the same frequency, a third oscillator which is adjustable in its frequency, means to combine the current of one of said standard oscillators with the current of said third oscillator to produce a current having a frequency equal to the difference between the frequencies of the currents combined, means to combine the current of the other of said standard oscillators with the current of the third oscillator to produce a current having a frequency equal to the difference between the frequencies of the combined currents, means to convert current resulting from the first combination into a direct current of an amplitude which varies with the variations in the frequency of the current resulting from said combination, means to convert the current resulting from the second combination into a direct current of an amplitude which varies in accordance with the variations in the frequency of the current resulting from the said combination, and means including a.

differential polar relay responsive to the greater of these direct currents to control the frequency of the third oscillator.

5. A frequency control system comprising an oscillator of adjustable frequency, two standard oscillators producing currents of the same frequencies, means coupled to the oscillator of adjustable frequency and one of said oscillators to produce a direct current of an amplitude corresponding to the difference between the frequencies of said oscillator of adjustable frequency and said standard oscillator, means coupled to the oscillator of adjustable frequency and the other of said standard oscillators to produce a direct current of an amplitude corresponding to the difference between the frequencies of said oscillator of adjustable frequency and said second oscillator, and means including a differential polar relay responsive to the greater of said direct currents to change the frequency of the current of said oscillator of adjustable frequency.

6. A frequency control system comprising two standard oscillators of variable frequency which are normally of the same value, an oscillator of adjustable frequency, a polar differential relay having two windings, means interconnecting said oscillator of adjustable frequency, one of said standard oscillators and one of the windings of said relay to transmit a current through said winding of the relay which varies in amplitude in accordance with the differences in the frequencies of said oscillators so interconnected, means interconnecting` said oscillator of adjustable frequency, the other of said standard oscillators and the second winding of said relay in order to transmit a current through said second winding of said relay which varies in accordance with the differences in the frequencies of said oscillators so interconnected, and means to increase the frequency of the current of said adjustable oscillator when the current through one of the windings of said relay exceeds the current through the other of said windings and to decrease the frequency of the current of said adjustable oscillator when the current through the first of said windings is less than that through the other of said windings.

In testimony whereof, I have signed my name to this specification this 15th day of February, 1930.

WILLIAM T. WINTRINGI-IAM. 

